Blow molding machines conventionally include an extruder that extrudes a tube of hot plastic between open sections of a mold. Closing of the mold then clamps the tube and allows air to be blown into the tube such that it assumes the shape of the mold. After suitable cooling has taken place, the mold sections are opened to allow ejection of the molded part.
Blow molded parts such as containers have conventionally included papers labels that are glued thereto after the molding to identify the contents of the container to the consumer. One problem with such paper labels is that they can become wrinkled if dampened and can also become detached from the container if a waterproof glue is not used. Also, paper labels require a separate labeling step after the molding which thus adds to the cost of the container.
In-mold labeling has been developed in the recent past for use with single cavity blow molding machines to provide superior bonding of labels to blow molded parts. This in-mold labeling is performed by inserting one or more labels within the mold prior to the extrusion of the hot plastic tube and subsequent closing of sections of the mold to enclose the plastic tube and each label within a single cavity of the mold in preparation for the blowing operation. The subsequent blowing operation forms the hot plastic tube around each label to the shape of the mold and activates a heat sensitive adhesive that provides a permanent bond which is incapable of being broken by moisture or otherwise. Also, such in-mold labeling provides a smooth transition between the label and the adjacent surface of the molded part and further provides additional strength since the label cooperates with the plastic in resisting deformation. Such strengthening also allows the use of less plastic to blow mold the part and thereby reduces the ultimate cost to the consumer. Furthermore, when utilized with containers for carbonated beverages, it is believed that in-mold labeling may reduce the flow of carbon dioxide out through the container wall over a period of time and thereby increases the shelf life.
Prior in-mold label dispensers for single cavity blow molding machines conventionally include a label carrier having vacuum cups that receive a label from a label magazine and then are movable to deposit the label within the mold cavity whereupon termination of a vacuum drawn at the cups allows a vacuum drawn at the mold cavity to secure the label in position in preparation for the molding. Such vacuum carriers have previously been mounted on pivotal arms that move in an angular path with respect to the direction of opening and closing movement of mold sections of the mold in order to permit depositing of the labels in the confined space permitted by the extent of the mold opening. With the pivotal arm type of label carrier, only one label can be deposited within the mold at a given time since movement thereof on the pivotal arm toward one mold section interferes with pivotal movement of a similar arm toward an opposed mold section for depositing another label.
Another prior art type of in-mold label dispenser for single cavity blow molding machines includes a label carrier that is moved along an abruptly curved path by a complex linkage which executes a 180 degree turn in order to transfer labels from a label magazine to the mold in preparation for molding. With this complex linkage type label dispenser, it is likewise not possible to deposit more than one label in the mold at a given time due to the limited space present upon opening of the mold.
Both of the prior art types of label dispensers described above for in-mold labeling of single cavity blow molding machines have an increased cycle time due to the necessity of depositing labels sequentially rather than at the same time.
Prior art in-mold labeling of single cavity blowing machines is disclosed by U.S. Pat. Nos.: 3,108,850; 3,151,193; 3,207,822; 3,227,787; 3,267,186; 3,272,681; 3,287,198; 3,292,209; 3,324,508; 3,608,020; 3,657,405; 3,674,391; 3,759,643; 3,759,645; 3,801,689; 4,355,967; and 4,359,314.
A further in-mold label dispenser which has been developed utilizes a dispensing head that is movable rectilinearly along a first axis to between open sections of a single cavity mold. At least one label carrier is mounted on the dispensing head for rectilinear movement along a second axis transverse to the first axis between retracted and extended positions. A label magazine associated with each label carrier supplies labels that are deposited within the mold cavity in preparation for the blow molding operation. With this dispenser, more than one label can be supplied to the mold at a given time to thus decrease the cycle time.
Blow molding machines with multiple cavity mold sections are also commercial used at the present time to simultaneously blow mold a plurality of parts. Heretofore, in-mold labeling of such multi-cavity blow molding machines has not been possible since no label dispenser has previously been developed for such machines.